I really do think that is true to some extent. I was that way too until I started including some powerlifting type training doing sets of 3-4 reps in heavy lifts like the squat. I found that in order for me to give 100% I had to grunt while pushing up the bar in the squat. I am always very quiet, but pusing yourself to the limit like that with heavy weight felt like it required me to grunt on at least the last rep on the set. I could normally do a set of 10 reps with 455 on the squat without making a peep. Doing a set with 525 or so and I found myself grunting pretty damn loud on the last 2 reps. Try a super intense set like that with a super heavy weight for you and see if you can stop yourself from grunting.
i agree, when i push hard, usually squat or dl i make a little noise. i workout alone so there's no attention im calling to myself...
...about planet fitness, if you don't like it, don't workout there. very simple.